Cooler Weather Signals Colorful Changes in Leaves

Cooler temperatures mean it is officially sweater weather in Kansas and time for fall festivities. For many, the truest indicator of autumn are the red, purple, yellow, orange and brown tree colors.

The pigments in the plant determine the individual color changes, said Ward Upham, Kansas State University horticulture expert. “Foliage derives its normal green color from chlorophyll, the substance that captures the energy of the sun. Other pigments produce fall colors.”

Anthocyanins cause red and purple leaves, xanthophylls result in yellow leaves, and oranges are a mix of carotenes and xanthophylls. Brown leaves are caused by tannins.

“Most of these substances are present throughout the growing season but are masked by the green color produced by chlorophyll,” Upham said. “Anthocyanins are the exception and are produced after the chlorophyll is destroyed in the fall.”

Color is also influenced by the weather, Upham said. Warm days filled with maximum sunlight followed by cool nights are ideal for radiant color.

“The sunny days encourage photosynthesis and, thus, sugar accumulation in the leaves,” he said. “Cool nights slow respiration, which helps conserve those sugars.”

High amounts of sugar in the leaves help produce more vibrant colors. Tree species also play a role in color variations.

“If you have ever seen pictures of New England in the fall, you have probably wondered why trees in Kansas usually do not color as well,” Upham said. “Certain oaks and maples naturally produce good color and are abundant in New England.”

Upham and his colleagues in K-State’s Department of Horticulture and Natural Resources produce a weekly Horticulture Newsletter with tips for maintaining home landscapes and gardens. The newsletter is available to view online or can be delivered by email each week.

Interested persons can also send their garden and yard-related questions to Upham at [email protected], or contact your local K-State Research and Extension office.


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